1. Field of the Invention
The present invention relates to a serial data transmission system for serially transmitting binary data over a plurality of transmission lines between a sending station and a receiving station.
1. Description of the Related Art
Serial data transfer systems have the disadvantage of having less bandwidth than parallel data transfer system. The bandwidth of a transmission line is the highest frequency that transitions can reliably be made on that transmission line.
Protocols have been devised for transmitting serial data over two lines for increasing the bandwidth of the transmission system. The IEEE-1394 data exchange protocol is such a two-wire system. The first line is a dedicated data line D on which a transition occurs each time the sequence of binary data changes value, that is the data sequence changes from a 1 to a 0 or from a 0 to a 1. The second line is a dedicated request line R on which two clock transitions occur during each binary data bit transmission period. An example of the IEEE-1394 protocol is shown in FIG. 5. The disadvantage with this protocol is that the highest data frequency that can be transmitted is equal to one half of the bandwidth for the transmission line being used.
The DS link protocol has been developed to overcome the bandwidth disadvantage of the IEEE-1394 protocol. The first line is a dedicated data line D on which a transition occurs each time the sequence of binary data changes value, that is the data sequence changes from a 1 to a 0 or from a 0 to a 1. The second line is a dedicated strobe line S on which a transition occurs each time the sequence of binary data does not change, that is the data sequence remains the same value a 1 to a 1 or a 0 to a 0. For every binary data bit transmission period either a transition will occur on the data line D or on the strobe line S. An example of the DS protocol is shown in FIG. 5. The DS protocol has the disadvantage that the highest data frequency is limited to the bandwidth of the transmission line being used.